South lhonak lake map

The South Lhonak Lake 

is situated in the state’s northwest at 17,000 ft. It formed due to the melting of the Lhonak glacier.

The outburst of the lake has caused the rise of water levels in Teesta river that flooded at least four districts, including Mangan, Gangtok, Pakyong and Namchi.

Lhonak lake is one of the largest and fastest growing proglacial lakes in Sikkim and is among the 11 large glacial lakes monitored by the Central Water Commission.

During the past 29 years, the glacier’s length has reduced from 6.4 km to 5.1 km.

The Lhonak lake, which measured just 0.17 square kilometres in 1977, grew to 0.78 square kilometres in 2002 and 1.35 square kilometres in 2019.

Between September 17 and September 28, its size shot up by around 5 hectares, which is around three percent of its size. 

What is GLOF?

Glacial Lakes are large bodies of water that sit in front of, on top of, or beneath a melting glacier. 

As they grow larger, they become more dangerous because glacial lakes are mostly dammed / Stop by unstable ice or sediment composed of loose rock and debris. 

In case the boundary around them breaks, huge amounts of water rush down the side of the mountains, which could cause flooding in the downstream areas. This is called glacial lake outburst floods or GLOF.

GLOF can be triggered by several reasons, including earthquakes, extremely heavy rains and ice avalanches.

These lakes are often found in steep, mountainous regions, which means landslides or ice avalanches can sometimes fall directly into the lakes and displace the water, causing it to over-top the natural dam and flood downstream.